xen: support sysenter/sysexit if hypervisor does

64-bit Xen supports sysenter for 32-bit guests, so support its
use.  (sysenter is faster than int $0x80 in 32-on-64.)

sysexit is still not supported, so we fake it up using iret.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

6 files changed, 99 insertions, 3 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 568c6ccd7ae..5d80d53eaff 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1017,6 +1017,13 @@ ENTRY(kernel_thread_helper)
 ENDPROC(kernel_thread_helper)
 
 #ifdef CONFIG_XEN
+/* Xen doesn't set %esp to be precisely what the normal sysenter
+   entrypoint expects, so fix it up before using the normal path. */
+ENTRY(xen_sysenter_target)
+        RING0_INT_FRAME
+        addl $5*4, %esp         /* remove xen-provided frame */
+        jmp sysenter_past_esp
+
 ENTRY(xen_hypervisor_callback)
         CFI_STARTPROC
         pushl $0
@@ -1036,8 +1043,17 @@ ENTRY(xen_hypervisor_callback)
         jae  1f
 
         call xen_iret_crit_fixup
+        jmp  2f
+
+1:      cmpl $xen_sysexit_start_crit,%eax
+        jb   2f
+        cmpl $xen_sysexit_end_crit,%eax
+        jae  2f
+
+        jmp xen_sysexit_crit_fixup
 
-1:      mov %esp, %eax
+ENTRY(xen_do_upcall)
+2:      mov %esp, %eax
         call xen_evtchn_do_upcall
         jmp  ret_from_intr
         CFI_ENDPROC
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 36f36e6b087..943684566eb 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -155,7 +155,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
         if (*ax == 1)
                 maskedx = ~((1 << X86_FEATURE_APIC) |  /* disable APIC */
                             (1 << X86_FEATURE_ACPI) |  /* disable ACPI */
-                            (1 << X86_FEATURE_SEP)  |  /* disable SEP */
                             (1 << X86_FEATURE_ACC));   /* thermal monitoring */
 
         asm(XEN_EMULATE_PREFIX "cpuid"
@@ -994,7 +993,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initdata = {
         .read_pmc = native_read_pmc,
 
         .iret = xen_iret,
-        .irq_enable_syscall_ret = NULL,  /* never called */
+        .irq_enable_syscall_ret = xen_sysexit,
 
         .load_tr_desc = paravirt_nop,
         .set_ldt = xen_set_ldt,
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 2341492bf7a..82517e4a752 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -16,6 +16,7 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
 
+#include <xen/interface/callback.h>
 #include <xen/interface/physdev.h>
 #include <xen/features.h>
 
@@ -68,6 +69,24 @@ static void __init fiddle_vdso(void)
         *mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
 }
 
+void xen_enable_sysenter(void)
+{
+        int cpu = smp_processor_id();
+        extern void xen_sysenter_target(void);
+        /* Mask events on entry, even though they get enabled immediately */
+        static struct callback_register sysenter = {
+                .type = CALLBACKTYPE_sysenter,
+                .address = { __KERNEL_CS, (unsigned long)xen_sysenter_target },
+                .flags = CALLBACKF_mask_events,
+        };
+
+        if (!boot_cpu_has(X86_FEATURE_SEP) ||
+            HYPERVISOR_callback_op(CALLBACKOP_register, &sysenter) != 0) {
+                clear_cpu_cap(&cpu_data(cpu), X86_FEATURE_SEP);
+                clear_cpu_cap(&boot_cpu_data, X86_FEATURE_SEP);
+        }
+}
+
 void __init xen_arch_setup(void)
 {
         struct physdev_set_iopl set_iopl;
@@ -82,6 +101,8 @@ void __init xen_arch_setup(void)
         HYPERVISOR_set_callbacks(__KERNEL_CS, (unsigned long)xen_hypervisor_callback,
                                  __KERNEL_CS, (unsigned long)xen_failsafe_callback);
 
+        xen_enable_sysenter();
+
         set_iopl.iopl = 1;
         rc = HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
         if (rc != 0)
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index e340ff92f6b..d61e4f8b07c 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -72,6 +72,7 @@ static __cpuinit void cpu_bringup_and_idle(void)
         int cpu = smp_processor_id();
 
         cpu_init();
+        xen_enable_sysenter();
 
         preempt_disable();
         per_cpu(cpu_state, cpu) = CPU_ONLINE;
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 99223cc323b..1ac08082a4b 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -280,6 +280,62 @@ ENTRY(xen_iret_crit_fixup)
 2:      ret
 
 
+ENTRY(xen_sysexit)
+        /* Store vcpu_info pointer for easy access.  Do it this
+           way to avoid having to reload %fs */
+#ifdef CONFIG_SMP
+        GET_THREAD_INFO(%eax)
+        movl TI_cpu(%eax),%eax
+        movl __per_cpu_offset(,%eax,4),%eax
+        mov per_cpu__xen_vcpu(%eax),%eax
+#else
+        movl per_cpu__xen_vcpu, %eax
+#endif
+
+        /* We can't actually use sysexit in a pv guest,
+           so fake it up with iret */
+        pushl $__USER_DS                /* user stack segment */
+        pushl %ecx                      /* user esp */
+        pushl PT_EFLAGS+2*4(%esp)       /* user eflags */
+        pushl $__USER_CS                /* user code segment */
+        pushl %edx                      /* user eip */
+
+xen_sysexit_start_crit:
+        /* Unmask events... */
+        movb $0, XEN_vcpu_info_mask(%eax)
+        /* ...and test for pending.
+           There's a preempt window here, but it doesn't
+           matter because we're within the critical section. */
+        testb $0xff, XEN_vcpu_info_pending(%eax)
+
+        /* If there's something pending, mask events again so we
+           can directly inject it back into the kernel. */
+        jnz   1f
+
+        movl PT_EAX+5*4(%esp),%eax
+2:      iret
+1:      movb $1, XEN_vcpu_info_mask(%eax)
+xen_sysexit_end_crit:
+        addl $5*4, %esp         /* remove iret frame */
+        /* no need to re-save regs, but need to restore kernel %fs */
+        mov $__KERNEL_PERCPU, %eax
+        mov %eax, %fs
+        jmp xen_do_upcall
+.section __ex_table,"a"
+        .align 4
+        .long 2b,iret_exc
+.previous
+
+        .globl xen_sysexit_start_crit, xen_sysexit_end_crit
+/*
+        sysexit fixup is easy, since the old frame is still sitting there
+        on the stack.  We just need to remove the new recursive
+        interrupt and return.
+ */
+ENTRY(xen_sysexit_crit_fixup)
+        addl $PT_OLDESP+5*4, %esp               /* remove frame+iret */
+        jmp xen_do_upcall
+
 /*
         Force an event check by making a hypercall,
         but preserve regs before making the call.
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 956a491ea99..01d4ff2ce40 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -19,6 +19,7 @@ extern struct shared_info *HYPERVISOR_shared_info;
 char * __init xen_memory_setup(void);
 void __init xen_arch_setup(void);
 void __init xen_init_IRQ(void);
+void xen_enable_sysenter(void);
 
 void xen_setup_timer(int cpu);
 void xen_setup_cpu_clockevents(void);
@@ -64,4 +65,6 @@ DECL_ASM(unsigned long, xen_save_fl_direct, void);
 DECL_ASM(void, xen_restore_fl_direct, unsigned long);
 
 void xen_iret(void);
+void xen_sysexit(void);
+
 #endif /* XEN_OPS_H */